This invention relates to a radar system and more particularly to electronic counter countermeasure means and a method of overcoming the effect of certain types of electronic countermeasures.
The great advances, made in the art of radar, inevitably led to the development of electronic countermeasures, known as ECM's, the primary purpose of which is to reduce and often destroy the effectiveness of even the most sophisticated radar system in detecting the locations of targets. One type of ECM is often referred to as the inverse gain sidelobe repeater. Basically, it is an electronic system which is carried aboard a target, such as an aircraft, which attempts to prevent a search radar from locating its position in azimuth. The repeater in essence includes a receiver which senses the energy patterns transmitted by the searching radar system and retransmits them, so that when they are received, they display the range, R, of the target but not its azimuth, A. That is, the target appears as if it is in all azimuths and therefore its azimuth location cannot be determined.
Another type of ECM is the standoff jammer. Unlike the inverse gain sidelobe repeater, the standoff jammer is not aboard an actual target but rather aboard another plane which generally accompanies a formation of targets. Its function is to generate electrical noise so that a relatively wide azimuth band on the display of the search radar is filled with noise signals which prevent the accurate detection of any targets therein in either range or azimuth. Alternately stated, the standoff jammer smears the radar display in a given azimuth band for all ranges to obscure the locations of any targets therein. Herebefore, the effect of a standoff jammer could not be countered effectively.
To overcome the effect of the inverse gain sidelobe repeater, a secondary or "guard" radar receiver with a separate antenna is employed, in addition to the primary radar system with its antenna. The output of the "guard" receiver is combined with the output of the receiver of the primary radar system. A system of detection logic is used to determine whether a received signal originated at the true angular location or azimuth of an ECM-carrying aircraft. Such a technique has been found to be quite complex and very costly since it is based on the need of an additional radar receiver and antenna.